Process for improving the chemical and/or physical properties of hollow-structure natural fibers

ABSTRACT

For improving the chemical and/or the physical properties of hollow-structure natural fibers, such as kapok fibers, the fibers are subjected to a process, which determines the internal coating and/or filling thereof, at least partly, with a substance capable of improving the chemical and/or the physical properties of the fibers.

The present invention refers to a process for improving the chemical and/or physical properties of hollow-structure natural fibers, preferably kapok fibers, to be used pure or mixed with natural animal fibers, plant fibers, synthetic polymeric fibers, man-made natural polymer fibers, continuous filaments of animal origin and/or discontinuous filaments of animal origin, for obtaining paddings, yarns, fabrics or non-woven fabric.

In the present invention, the expression weave is generally used for distinguishing the warp and weft and for distinguishing the weave for knitted garments.

In the present description, by way of example:

-   -   animal fibers are intended to cover fleece or hair fibers (such         as wool, alpaca, vicuna, cashmere and others);     -   continuous filaments of animal origin are intended to cover         filaments obtained by reeling from whole cocoons (such as silk);     -   discontinuous filaments of animal origin are intended to cover         filaments obtained by unravelling from defective cocoons (such         as waste silk);     -   vegetable fibers are intended to cover all the fibers obtained         from plants, shrubs, inflorescences, roots, leaves (such as         cotton, flax, hemp, jute, coir, ramie, bamboo, and others);     -   the expression synthetic polymeric fibers is used to indicate,         for example, the polyamide, polyester, acrylic, polypropylene         fibers etc.;     -   man-made natural fibers are intended to cover, for example,         rayon viscose, modal, acetate, cupro, tencell, and others and     -   the expression long fibers is used to indicate fibers having a         length of at least 0.01 m (i.e. 1 cm), such fibers being         suitable to be used for various subsequent processes, such as         for example spinning.

In order to obtain paddings, yarns, non-woven fabric there is known the use of various types of fibers, used pure or mixed to each other, with the aim of obtaining products having the desired chemical/physical properties.

Thus, for example, in case of padding, whether for a couch or jacket, the characteristic of the fiber used for obtaining the padding being light, resistant, so as to return to the initial state after being compressed by a load, and possibly being antibacterial, disinfectant and the like is very appreciated.

Analogous considerations may be referred to yarns or fabrics made using natural fibers, with addition, in this case, of the characteristic of fibers of being soft besides light.

In the light of the above, it is clear that today there strongly arises the need of being able to improve the chemical/physical properties of natural fibers, such as the kapok or ordinary animal hair wools, to be used pure or mixed with natural animal fibers, plant fibers, synthetic polymeric fibers, man-made natural polymer fibers, continuous filaments of animal origin and/or discontinuous filaments of animal origin, for obtaining paddings, yarns, fabrics or non-woven fabric.

The problem on which the present invention is based is that of devising and providing a process for improving the chemical and/or physical properties of hollow-structure natural fibers, to be used pure or mixed with natural animal fibers, plant fibers, synthetic polymeric fibers, man-made natural polymer fibers, continuous filaments of animal origin and/or discontinuous filaments of animal origin, for obtaining paddings, yarns, fabrics or non-woven fabric, thus the process allowing meeting the aforementioned need.

Such problem is overcome by a process for improving the chemical and/or physical properties of hollow-structure natural fibers according to claim 1.

According to a further aspect, the invention also addresses the use of hollow-structure natural fibers according to claim 19, as well as the use of kapok fibers according to claim 20.

According to the invention, the hollow-structure natural fibers are internally coated, at least partly, and/or filled, at least partly, with a substance suitable to improve the chemical and/or physical properties of the hollow-structure natural fibers with the aim of improving the chemical and/or physical properties of said hollow-structure natural fibers.

Further characteristics and advantages of the process according to the present invention shall be apparent from the description provided hereinafter regarding some of its preferred embodiments, provided by way of non-limiting example, with reference to the attached figures, wherein:

-   -   FIGS. 1 and 2 each show an image of a kapok fiber analyzed using         a scan electron microscope (SEM) before being processed with the         process according to the invention;     -   FIGS. 3 and 4 each show an image of a kapok fiber analyzed using         a scan electron microscope (SEM) after being processed with the         process according to the invention and

FIG. 5 shows images of kapok fibers analyzed using an optical microscope with a 100× enlargement during the processing step using the process according to the invention.

The process for improving the chemical and/or physical properties of hollow-structure natural fibers comprises the steps of:

-   -   preparing hollow-structure natural fibers of animal or plant         origin to be used pure or mixed with natural animal fibers,         plant fibers, synthetic polymeric fibers, man-made natural         polymer fibers, continuous filaments of animal origin and/or         discontinuous filaments of animal origin, in which the interior         cavities of said hollow-structure natural fibers are in fluid         communication with the exterior and     -   preparing a substance suitable to improve the chemical and/or         physical properties of the aforementioned hollow-structure         natural fibers.

Advantageously, the process according to the invention is characterized in that it comprises a step for internally coating, at least partly, and/or filling, at least partly, the aforementioned hollow-structure natural fibers with the aforementioned substance, or with several substances, with the aim of obtaining an improvement of the chemical and/or physical properties of the hollow-structure natural fibers.

According to a preferred embodiment, the aforementioned hollow-structure natural fibers comprise, or are constituted, by kapok fibers to be used for obtaining paddings, yarns, fabrics or non-woven fabric pure or mixed with natural animal fibers, plant fibers, synthetic polymeric fibers, man-made natural polymer fibers, continuous filaments of animal origin and/or discontinuous filaments of animal origin, after being treated with the process according to the present invention.

As result from FIGS. 1 and 2, the kapok fibers have a hollow tubular structure, which is open at the opposite ends. Thus, the kapok fibers are suitable to be at least partly internally coated and/or filled as indicated hereinafter.

As an alternative to kapok, as hollow-structure natural fibers, with the cavities in fluid communication with the outside, there can also be used other fibers, possibly mixed with kapok or with other fibers. For example, it is possible to use ordinary animal hair wool, i.e. animal hair wool having fibers with large diameters, which are at least partly hollow, with the cavities in fluid communication with the outside.

According to a preferred embodiment, the process according to the invention comprises a step of preparing a solution, or bath, comprising the aforementioned substance, so that the aforementioned step of internally coating, at least partly, and/or internally filling, at least partly, the aforementioned hollow-structure natural fibers is carried out by submerging the hollow-structure natural fibers in the prepared solution.

As regards the aforementioned solution, or bath, it should be observed that, it preferably has a pH value comprised between 4 and 7, more preferably a pH value comprised between 4.5 and 7.

Furthermore, it should be observed that the aforementioned substance for improving the chemical and/or physical properties of the hollow-structure natural fibers is present in the solution with a concentration of 0.5-15% w/v, more preferably with a concentration of 1-7% w/v.

The aforementioned substance used for internally coating, at least partly, and/or internally filling, at least partly, the aforementioned hollow-structure natural fibers may be selected from the group comprising: chitosan and/or its derivatives, antibacterial substances, substances efficient against acari, disinfectant substances, perfuming substances, substances for increasing the resilience of the fibers and/or substances for increasing the resistance of the fibers against breakage.

Chitosan is a natural polymer derived from chitin, a protein contained in the exoskeleton of crustaceans, and it is made of material renewable in nature given that it can be obtained from the food industry by-products. Following various experimental tests, it was observed that a chitosan, a chitosan oligomer or other chitosan derivatives, all having a medium or preferably low molecular weight, is advantageous as a substance for improving the chemical and/or physical properties of the hollow-structure natural fibers.

According to a preferred embodiment, the aforementioned substance for improving the chemical and/or physical properties of the hollow-structure natural fibers comprises, or it is constituted, by chitosan, chitosan oligomer and/or chitosan derivatives having a molecular weight less than 200,000 Da, more preferably having a molecular weight less than 100,000 Da and, even more preferably, having a molecular weight of 1,000-50,000 Da.

For example in the case where the aforementioned substance was chitosan, chitosan oligomer or another chitosan derivative, there was obtained an optimal result, in terms of increase of resilience and resistance of the treated fibers, as well as in terms of high antibacterial characteristics, disinfectant characteristics and efficiency against the acari fibers treated using a chitosan, a chitosan oligomer or any other chitosan derivative all having a molecular weight in the order of 2,000 Da, or lesser.

The concentrations of chitosan in the liquid solution used were in the order of 1% w/v or higher, given that good results were verified with a concentration of chitosan up to 15% w/v or up to 20% w/v.

The attained results were very good with the use of chitosan, chitosan oligomer and/or with low viscosity chitosan derivatives, for example a chitosan, a chitosan oligomer and/or a chitosan derivative all having a molecular weight of 1,000-5,000 Da, preferably having a molecular weight in the order of 1,000-2,000 Da.

In addition to the above, it should be observed that the filling and the ensuing coating of the hollow-structure of the natural fibers are particularly problematic when the fibers are long fibers, i.e. fibers having a length at least in the order of 0.01 m (i.e. 1 cm).

This depends on the fact that the internal cavity of the hollow-structure natural fibers identifies an actual capillary, whose transverse section dimension is infinitely smaller than the axial length. Such configuration constitutes a hindrance to the filling—with the solution, or bath, comprising the aforementioned substance—of the interior cavity of natural fibers over the entire axial length of the fibers. Thus, in case of long fibers, only a short end section of the hollow-structure natural fibers is filled and it is coated at the end of the process.

Regarding this, it should be observed that, generally, the fibers used for obtaining paddings or yarns should be long fibers in the sense defined above, given that too short fibers are not suitable for spinning and they are not even suitable for obtaining paddings and the like.

For example, natural fibers cut into pieces having an axial length lesser than 0.005 m (i.e. 5 mm) are not suitable for the purpose.

With the aim of overcoming the aforementioned drawbacks, according to a further aspect of the process according to the invention, there is provided for a step during which the hollow-structure natural fibers are processed using ultrasounds while they are submerged in the aforementioned liquid solution, or bath. Basically, there is obtained a stirring, using ultrasounds, of the solution in which the hollow-structure fibers are submerged, also obtaining a better dispersion in the solution, or bath of the various components. The aforementioned step of processing through ultrasound may, for example, be attained by submerging an ultrasound emission probe in the aforementioned solution, or bath.

It should be observed that the ultrasounds, due to their frequency, for example in the order of 20 KHz, induce a sort of vibration in the liquid solution which determines a micro cavitation effect with partial implosion of the bubbles that form in the liquid solution, thus determining a more efficient penetration of the liquid solution and substance, or substances, therein contained inside the cavities of the natural fibers being processed, without causing any damage to the hollow-structure of the natural fibers thus processed.

As observed by way of experiment, the aforementioned ultrasound processing in solution, or bath, determines an optimal filling even of long fibers, for example hollow-structure natural fibers, in particular kapok, having an axial length even greater than 1 cm, for example in the order of 3-5 cm, such treatment advantageously allowing coating the internal hollow-structure over the entire extension thereof.

The solution, or bath, into which there are submerged the hollow-structure fibers whose chemical and/or physical properties are to be improved may be of the aqueous base type, or based on other solvents (both of the polar and non-polar type).

The time for the ultrasound processing of hollow-structure fibers whose chemical and/or physical properties are to be improved may be in the order of 10-70 minutes.

The power of the ultrasounds to be used for the treatment on the hollow-structure fibers whose chemical and/or physical properties are to be improved may be in the order of 100-750 Watt.

According to a preferred and advantageous embodiment, the aforementioned step of submerging the hollow-structure natural fibers—whose chemical and/or physical properties are to be improved—in the solution containing the aforementioned substance is preceded by a step of subjecting hollow-structure natural fibers to vacuum. Basically, before being submerged in the aforementioned liquid solution, the hollow-structure natural fibers are brought to an external pressure below the atmospheric pressure, for example at a pressure comprised between 20% and 90% of the atmospheric pressure, preferably a pressure comprised between 30% and 80% of the atmospheric pressure.

In the experiments, there were obtained optimal results taking the hollow-structure natural fibers to be processed up to very high depressions with respect to the atmospheric pressure.

It should be observed that, in this case, the aforementioned step of submerging the hollow-structure fibers is liquid solution is obtained starting from an initial condition in which the fibers to be submerged are at an external pressure lesser than the atmospheric pressure. By way of example, this can be obtained by preparing a sealingly closed container provided with:

-   -   an inlet connected through first closure/interception valve         means with a vacuum pump or other equivalent means, as well as     -   an inlet connected through second closure/interception valve         means with a tank containing the solution in which the         hollow-structure fibers to be treated are submerged.

The hollow-structure fibers to be treated are positioned in the aforementioned sealingly closed container. Subsequently the first valve means are opened and the vacuum pump is actuated up to obtaining, inside the container, the desired pressure value lesser than the atmospheric pressure. Subsequently, the first valve means are closed and the second valve means are closed, determining the entry of the liquid solution containing the aforementioned substance for improving the chemical and/or physical properties of the hollow-structure natural fibers into the container. Thus, the hollow-structure natural fibers contained in the container are submerged in the liquid solution while they are in an environment with pressure below the atmospheric pressure. This determines a greater penetration of the liquid solution in the cavities of the natural fibers, particularly when the pressure in the container is brought to the atmospheric pressure value.

Preferably, the process according to the invention comprises a step of drying the hollow-structure natural fibers carried out, for example in an oven, after the hollow-structure natural fibers were removed from the liquid solution.

The aforementioned drying, which can be carried out through the ventilation of hot air or through to a different drying method, may be extended up to obtaining a complete drying of the hollow-structure natural fibers, with ensuing adhesion of the substance contained in the dried solution to the walls of the hollow-structure natural fibers. Thus, even the internal walls of the cavities of the natural fibers are at least partly coated/covered, preferably completely coated/covered, with the aforementioned substance added in the solution, as observable in FIGS. 3 and 4.

The drying of the fibers may be conveniently carried out at a temperature comprised between 60° C. and 105° C.

FIG. 5 shows some hollow-structure natural fibers while submerged in the solution containing the substance, outlining the previously attained partial filling of the tubular cavities using the liquid solution.

Should the aforementioned substance added in the solution for improving the chemical and/or physical properties of the hollow-structure natural fibers be chitosan, chitosan oligomer and/or a chitosan derivative, there can be provided for a step of chemical cross-linking and/or through chitosan ultraviolet rays, chitosan oligomer and/or chitosan derivative applied to the hollow-structure natural fibers.

This allows obtaining a permanent adhesion of chitosan, chitosan oligomer and/or chitosan derivative to the treated hollow-structure natural fibers, guaranteeing the duration of the beneficial effects over time due to the presence of chitosan even following several wash cycles or further fixing steps such as dying.

In addition, the crosslinking of chitosan, chitosan oligomer and/or chitosan derivatives allows conferring the treated hollow-structure natural fibers greater mechanical physical resistance besides a long-lasting disinfection effect efficient against acari.

The aforementioned cross-linking of chitosan, chitosan oligomer and/or a chitosan derivative may advantageously be obtained physically, for example by exposure to ultraviolet rays, or chemically, for example by adding citric acid and/or acrylic monomers, for example HEMA, to the solution where the hollow-structure natural fibers to be treated are submerged.

It should be observed that while the cross-linking of chitosan, chitosan oligomer and/or chitosan derivative through exposure to ultraviolet rays is only efficient on the chitosan present on the external of the treated natural fibers, the chemical cross-linking by adding suitable substances to the solution in which the hollow-structure natural fibers are submerged is efficient even as regards chitosan, chitosan oligomer and/or chitosan derivative which are adhered to the natural fibers in the cavities.

It is clear that the at least partial coating of the walls of the internal cavities of the natural fibers substantially allows doubling the adsorbing surface of the treated hollow-structure natural fibers. This is particularly useful to obtain filters in which the filtering elements comprise the treated hollow-structure natural fibers.

According to a further aspect, the substance to be penetrated into the cavities of the natural fibers may be carried/loaded by cyclodextrins, nanocapsules and/or microcapsules.

In the light of the above, it is clear that the process according to the invention described above, allows meeting the need subject of reference in the initial part of the present description, given that it allows internally coating, at least partly, and/or filling, at least partly, the hollow-structure natural fibers treated with the substance, or substances, capable of improving the chemical and/or physical properties of the aforementioned hollow-structure natural fibers.

What has been described above is susceptible to numerous modifications and variants, all falling within the inventive concept identified by the following claims.

In addition, the use of kapok as the hollow-structure natural fiber is extremely advantageous not only as regards the fact that kapok fibers have a hollow tubular configuration open at the ends, being suitable to be coated or filled internally, but also due to the fact that kapok fibers are extremely light, soft.

As described above, the hollow-structure natural fibers, in particular kapok, are suitable to be used for obtaining paddings, yarns, fabrics or non-woven fabric, pure or mixed with natural animal fibers, plant fibers, synthetic polymeric fibers, man-made natural polymer fibers, continuous filaments of animal origin and/or discontinuous filaments of animal origin.

The use of the aforementioned hollow-structure natural fibers mixed with other types of fibers allows obtaining a mixture of fibers with optimal characteristics. 

1-21. (canceled)
 22. A process for improving at least one of chemical or physical properties of hollow-structure natural fibers, the process comprising: providing the hollow-structure natural fibers of animal or vegetable origin to be used either pure or blended together with animal natural fibers, vegetable fibers, polymeric synthetic fibers, man-made natural polymer fibers, continuous filaments of animal origin and/or discontinuous filaments of animal origin, and internal cavities of the hollow-structure natural fibers being in fluid communication with an outside, providing a substance suitable for improving at least one of the chemical or the physical properties of the hollow-structure natural fibers, and at least partially internally coating and/or of at least partially filling of the hollow-structure natural fibers with the substance in order to obtain an improvement in at least of the chemical or the physical properties of the hollow-structure natural fibers.
 23. The process according to claim 22, further comprising using fibers which have a length of at least 0.01 m as the hollow-structure natural fibers.
 24. The process according to claim 22, comprising preparing a solution comprising the substance, and carrying out the at least partially internally coating and/or of at least partially filling of the hollow-structure natural fibers through immersion of the hollow-structure natural fibers in the solution.
 25. The process according to claim 24, comprising subjecting the hollow-structure natural fibers to ultrasound treatment during the immersion in the solution.
 26. The process according to claim 25, further comprising subjecting the hollow-structure natural fibers to a vacuum so as to take the hollow-structure natural fibers to an external pressure below atmospheric pressure, prior to the immersion of the hollow-structure natural fibers in the solution containing the substance, and carrying out the immersion of the fibers in the solution while the hollow-structure natural fibers are maintained at the external pressure below atmospheric pressure.
 27. The process according to claim 26, further comprising using a pressure of between 20% and 90% of atmospheric pressure as the pressure below atmospheric pressure.
 28. The process according to claim 25, comprising drying/desiccating the hollow-structure natural fibers, after the removal of the hollow-structure natural fibers from the solution, so as to adhere the substance to the hollow-structure natural fibers.
 29. The process according to claim 24, wherein the solution has a pH value of between 4 and
 7. 30. The process according to claim 25, wherein the substance is present in the solution at a concentration 0.5-15% w/v.
 31. The process according to claim 25, wherein the substance is selected from the group consisting of: chitosan, chitosan oligomer and/or chitosan derivatives.
 32. The process according to claim 31, wherein the substance is chitosan, chitosan oligomer and/or chitosan derivatives which have a molecular weight of less than 200,000 Da.
 33. The process according to claim 31, wherein the substance is chitosan, chitosan oligomer and/or chitosan derivatives which have a molecular weight of 1,000-5,000 Da.
 34. The process according to claim 31, further comprising at least one of a chemical and an ultraviolet ray cross-linking of the chitosan, of the chitosan oligomer and/or of the chitosan derivatives applied to the hollow-structure natural fibers.
 35. The process according to claim 24, further comprising ensuring the chemical cross linking of the chitosan, of the chitosan oligomer and/or of the derivatives by addition of citric acid and/or of acrylic monomers to the solution.
 36. The process according to claim 22, wherein the substance is selected from the group consisting of: anti-bacterial substances, anti-acari substances, sanitizing substances, perfuming substances, substances to increase a resilience of the fibers and/or substances to increase a breaking resistance of the fibers.
 37. The process according to claim 22, further comprising carrying the substance via cyclodextrin, nanocapsules and/or microcapsules.
 38. The process according to claim 22, further comprising using kapok fibers as the hollow-structure natural fibers.
 39. The process according to claim 22, further comprising using coarse wools of animal hair as the hollow-structure natural fibers,
 40. Use of hollow-structure natural fibers, wherein the internal cavities of the natural fibers are in fluid communication with the outside, pure or blended together with animal natural fibers, vegetable fibers, polymeric synthetic fibers, man-made natural polymer fibers, continuous filaments of animal origin and/or discontinuous filaments of animal origin, for making paddings, yarns, fabrics or unwoven fabrics, wherein the hollow-structure natural fibers are at least partially internally coated and/or at least partially filled by the process according to claim
 25. 41. The use of kapok fibers, pure or blended together with animal natural fibers, vegetable fibers, polymeric synthetic fibers, man-made natural polymer fibers, continuous filaments of animal origin and/or discontinuous filaments of animal origin, for making paddings, yarns, fabrics or unwoven fabrics, wherein the kapok fibers are at least partially internally coated and/or at least partially filled by the process according to claim
 25. 42. The use of hollow-structure natural fibers according to claim 40, wherein the hollow-structure natural fibers have a length of at least 0.01 m.
 43. The use of hollow-structure natural fibers according to claim 41 wherein the hollow-structure natural fibers have a length of at least 0.01 m. 